February 2026

Dermal detective

​A 2-year-old neutered male mixed breed dog from Pennsylvania was presented to a veterinarian for evaluation of a dermal mass (~ 1cm) in the left forelimb. The mass was noticed a week prior.  The veterinarian recommended a biopsy, and the following was observed (Images 1 and 2).

Thank you to Dr. Kelly Mitchell for submitting the case to Oklahoma State University and to Dr. Kathryn Duncan for sharing.

Image 1 and 2: Histological section of dermal mass from left forelimb.

What's your diagnosis?

Spirometra sp. plerocercoid. 

Spirometra spp. are cestodes that usually develop as adults in the small intestine of cats and dogs and release undeveloped eggs in the feces.  A larval stage (coracidia) grows within the egg for about 1 or 2 weeks and is released into the water. If copepods ingest this larva, an embryo called procercoid develops in the body cavity of the copepod. Typically, these copepods are ingested by various vertebrates (except fish) that act as second intermediate hosts where the final infective stage develops as plerocercoids.  Plerocercoids are in the subcutaneous tissues of these vertebrates and when ingested by a dog or cat they develop into adults. 

On some occasions dog or cats can develop plerocercoids (Sparagna) by 1)drinking water contaminated with infected copepods, 2) ingesting plerocercoid form vertebrate hosts or 3) direct infection of open wounds with plerocercoids.

​Sparganosis can be presented as non-proliferative or proliferative, in this case it was diagnosed as non-proliferative.  It is important to mention that sparganosis is a zoonosis, therefore preventive measures should be adopted to avoid consumption of contaminated water or food.